The present invention generally relates to rollover sensors and, more particularly, to vehicle rollover sensing with minimal sensor hardware for sensing a rollover condition of a vehicle.
Automotive manufacturers are increasingly equipping vehicles with safety-related devices that deploy in the event that the vehicle experiences a rollover so as to provide added protection to the occupants of the vehicle. For example, upon detecting a vehicle rollover event, a pop-up roll bar can be deployed such that, when activated, the roll bar further extends vertically outward to increase the height of support provided by the roll bar during the rollover event. Other controllable devices may include the deployment of one or more air bags, such as frontal air bags, side mounted air bags, and roof rail air bags, or actuating a pretensioner to pretension a restraining device, such as a seatbelt or safety harness, to prevent occupants of the vehicle from ejecting from the vehicle or colliding with the roof of the vehicle during a rollover event.
Mechanical-based rollover sensors have been employed in automotive vehicles to measure the angular position of the vehicle exceeding a predetermined threshold from which a rollover event can be determined. The mechanical sensors typically have included the use of a pendulum normally suspended vertically downward due to the Earth""s gravitational force. Many mechanical automotive sensing devices have been employed simply to monitor the angular position of the vehicle relative to a horizontal level ground position which is generally perpendicular to the gravitational force vector. As a consequence, such mechanical automotive sensors have generally been susceptible to error when the vehicle travels around a corner or becomes airborne, in which case the Earth""s gravitational force, which the sensor relies upon, may be overcome by dynamic forces.
More sophisticated rollover sensing approaches generally require the use of as many as six sensors including three accelerometers and three angular rate sensors, also referred to as gyros, and a microprocessor for processing the sensed signals. The three accelerometers typically provide lateral, longitudinal, and vertical acceleration measurements of the vehicle, while the three gyros measure angular pitch rate, roll rate, and yaw rate. Such sophisticated rollover sensing approaches generally require a large number of sensors which add to the cost and complexity of the overall system. In addition, known sophisticated systems are generally susceptible to cumulative drift errors.
Some rollover sensing approaches have attempted to minimize the number of sensors required for rollover detection. For rollover sensing about a single axis, some traditional sensing approaches employ a combination of three or four individual sensors, depending upon the rollover algorithm employed. Other sensing approaches have attempted to employ, at a minimum, both an angular rate sensor and an accelerometer, either in the lateral axis or vertical axis. While the angular rate sensor output can ideally be integrated over time to estimate the vehicle roll angle, in practice, such sensors typically have a non-zero, time-varying output, even when no roll rate is present. This sensor bias may cause a significant error in the integrated roll angle, and therefore the sensed signals must be compensated to remove the error. Accelerometers are often used to provide such compensation; however, automotive-grade low-G accelerometers are generally expensive, and accelerometer bias and offset errors also need to be compensated for, possibly by some costly means of calibration during the manufacturing process.
Accordingly, it is desirable to provide for an accurate and timely rollover sensing approach that minimizes the number of sensors that are required to detect rollover of a vehicle. More particularly, it is desirable to provide for a rollover detection approach that allows for use of angular rate sensors, without requiring auxiliary sensors in addition thereto. It is further desirable to provide for such a rollover sensing approach that eliminates the need for low-G accelerometers.
In accordance with the teachings of the present invention, a vehicle rollover sensor and method are provided for detecting an anticipated overturn condition of a vehicle, thus allowing for timely deployment of safety-related devices. The rollover sensor includes a first angular rate sensor for sensing attitude rate of change of a vehicle about a first axis and producing a first attitude rate of change signal indicative thereof. Also included is a second angular rate sensor for sensing attitude rate of change of the vehicle about a second axis and producing a second attitude rate of change signal indicative thereof. The first and second angular rate sensors are located on the vehicle and arranged so that the first axis is different from the second axis. The rollover sensor further includes a rollover discrimination controller for determining a vehicle overturn condition based on the first and second sensed attitude rate of change signals and providing an output signal indicative thereof.
According to another aspect of the present invention, the rollover sensor includes a first angular rate sensor for sensing a first attitude rate of change of a vehicle and producing a first attitude rate of change signal, and a second angular rate sensor for sensing a second attitude rate of change of the vehicle and producing a second attitude rate of change signal. Rollover arming logic receives the first and second attitude rate of change signals and generates a roll arming signal as a function of the first and second attitude rate of change signals. A rollover discrimination controller generates a vehicle overturn condition signal as a function of the first and second attitude angles and the rollover arming signal.
According to a further aspect of the present invention, a method is provided for detecting an anticipated overturn condition of a vehicle. The method includes the steps of sensing attitude rate of change of a vehicle about a first axis and producing a first attitude rate of change signal indicative thereof, and sensing attitude rate of change of the vehicle about a second axis and producing a second attitude rate of change signal indicative thereof, wherein the first axis is different from the second axis. The method further includes the step of determining a vehicle overturn condition based on the first and second sensed attitude rate of change signals. According to yet a further aspect of the present invention, the method includes a step of determining a roll arming signal based on the first and second sensed attitude rate of change signals, wherein the vehicle overturn condition is determined further as a function of the roll arming signal.
Accordingly, the rollover sensor and method of the present invention advantageously minimizes the number of sensors that are required to arm and discriminate an overturn (rollover and/or pitchover) condition of a vehicle. It should be appreciated that the rollover sensor and method employ first and second angular rate sensors, without requiring other auxiliary sensors, to achieve cost-efficient and accurate vehicle rollover detection.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.